Image sensor of fingerprint

ABSTRACT

An image sensor includes a sensor layer and at least one metal layer. The sensor layer includes a plurality of sensing elements arranged as a 2-dimensional array along a first direction and a second direction. Each of the at least one metal layer includes a plurality of metal wires configured to form a plurality of apertures for passing lights to the plurality of sensing elements. At least one of the plurality of metal wires forming the plurality of apertures is disposed along a third direction different from the first direction and the second direction.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/779,489, filed on Dec. 14, 2018, the contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to an image sensor, and more particularly,to an image sensor of fingerprint.

2. Description of the Prior Art

With advancements in technology, mobile devices such as smart phones,tablets, laptops, GPS navigation systems and electronic books havebecome indispensable in our daily life. Compared with conventionalmobile phones that only have communication functions, modern mobiledevices combine various functions such as communication, networking,photographing, games and data processing. This type of multifunctionaldesign is more attractive to consumers. Fingerprint recognition is apopular function for security and privacy in various electronic devices,including mobile devices, and can be implemented in different techniquessuch as capacitance sensing, optical (image sensing), thermal,ultrasonic, etc. For example, a mobile phone may have a fingerprintrecognition interface built into a home button or in a dedicated regionto detect user fingerprint.

In recent years, the optical fingerprint recognition has become one ofthe most popular fingerprint recognition schemes. Please refer to FIG.1, which is a schematic diagram of the structure of an opticalfingerprint recognition system 10. The optical fingerprint recognitionsystem 10 includes a touch panel 102, at least one lens 104 and a sensorintegrated circuit (IC) 106. The touch panel 102 is configured tocontact the finger of a user to receive the fingerprint image. The imageis then forwarded to the sensor IC 106 via the lens 104. In general, ifthe optical fingerprint recognition system 10 is integrated with adisplay device such as an organic light-emitting diode (OLED) panel, thepanel structure of the display device may be superposed on the lens 104or the sensor IC 106, to interfere with the sensed fingerprint image,e.g., blocking parts of the light reflected from the touch finger. Inother words, the light reflected from the touch finger may pass throughdevices in the image pixel array of the OLED and then be sensed by thesensing pixels included in the sensor IC 106.

In general, each pixel of the display panel has the same structure, togenerate a plurality of light paths having similar texture arranged asan array. The sensing pixels in the sensor IC 106 are also arranged asan array, and each sensing pixel has a sensing area capable of receivinglights. If the dimensions of the image pixel array of the display deviceare close to the dimensions of the sensing pixel array of the sensor IC106, moire pattern may appear since the light sensed by the sensor IC106 passes through grille patterns of both the display panel and thesensing area. The moire effect degrades the quality and resolution ofthe fingerprint image. FIG. 2 illustrates an exemplary fingerprint imageinterfered with the moire pattern, where redundant arc lines other thanthe fingerprint may appear.

In order to mitigate the problem of moire pattern, the die of the sensorIC 106 may be disposed with a turning angle in the package module, asshown in FIG. 3. However, the turning disposition scheme results insignificant increasing of chip size. In an example as shown in FIG. 3,the die size is 18.69 mm×11.31 mm, and the total chip size including thepackage is 20.9 mm×15.24 mm, where the chip area is expanded since thedie is disposed with a turning angle. Thus, there is a need forimprovement over the prior art.

SUMMARY OF THE INVENTION

It is therefore an objective of the present invention to provide afingerprint image sensor, which is capable of solving the problem ofmoiré pattern without increasing the chip size of the sensor integratedcircuit (IC).

An embodiment of the present invention discloses an image sensor, whichcomprises a sensor layer and at least one metal layer. The sensor layercomprises a plurality of sensing elements arranged as a 2-dimensionalarray along a first direction and a second direction. Each of the atleast one metal layer comprises a plurality of metal wires configured toform a plurality of apertures for passing lights to the plurality ofsensing elements. At least one of the plurality of metal wires formingthe plurality of apertures is disposed along a third direction differentfrom the first direction and the second direction.

Another embodiment of the present invention discloses an image sensor,which comprises a sensor layer and at least one metal layer. The sensorlayer comprises a plurality of sensing elements arranged as a2-dimensional array along a first direction and a second direction. Eachof the at least one metal layer comprises a plurality of metal wiresconfigured to form a plurality of apertures for passing lights to theplurality of sensing elements. A border of the plurality of sensingelements is disposed along a third direction different from the firstdirection and the second direction.

Another embodiment of the present invention discloses an image sensor.The image sensor comprises a sensor layer and at least one metal layer.The sensor layer comprises a plurality of sensing elements divided intoa plurality of groups, wherein the plurality of groups are arranged as a2-dimensional array along a first direction and a second direction. Eachof the at least one metal layer comprises a plurality of metal wiresconfigured to form a plurality of apertures for passing lights to theplurality of sensing elements. The sensing elements in each of theplurality of groups are arranged as a 2-dimensional array along a thirddirection and a fourth direction, wherein each of the third directionand the fourth direction is different from the first direction and thesecond direction.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of the structure of an optical fingerprintrecognition system.

FIG. 2 illustrates an exemplary fingerprint image interfered with themoiré pattern.

FIG. 3 is a schematic diagram of a package module including the sensorIC.

FIG. 4 is a schematic diagram of an image sensor according to anembodiment of the present invention.

FIG. 5 is a schematic diagram of another image sensor according to anembodiment of the present invention.

FIG. 6 is a further image sensor according to an embodiment of thepresent invention.

DETAILED DESCRIPTION

As mentioned above, the chip size increases because the die is turned byan angle inside the package module. In order to effectively mitigate themoiré effect, the die should be turned by at least 15 degrees, and hencethe increasing area becomes significant.

In order to deal with the moiré effect while maintaining the chip sizeat a satisfactory level, the present invention turns the sensing elementin each pixel or turns the metal layers forming the sensing light pathinstead of turning the die. In such a situation, the interference ofmoiré pattern on the fingerprint image may be mitigated or eliminated,and there is no need to turn the disposition of die inside the packagemodule, allowing the sensor integrated circuit (IC) to have a smallerchip size.

Please refer to FIG. 4, which is a schematic diagram of an image sensor40 according to an embodiment of the present invention. As shown in FIG.4, the image sensor 40, which may be a sensor IC, includes a pluralityof sensing pixels arranged as a 2-dimensional array. For the purpose ofsimplicity, only 4 sensing pixels are illustrated. Nevertheless, thoseskilled in the art should understand that there may be hundreds orthousands of sensing pixels in the image sensor 40. Each sensing pixelincludes a sensing element such as a photodiode, which is capable ofreceiving lights and converting lights into electrons. The electrons maybe outputted in the form of any electronic signals such as voltages orcurrents and then be converted into digital image data to be processedby a processor or host device so as to construct the fingerprint image.Each sensing pixel further includes a light sensing area that may bedefined by an aperture formed by metal wires. In other words, the imagesensor 40 includes a sensor layer and at least one metal layer, wherethe sensor layer has the sensing elements in the pixels, and the metallayer includes metal wires configured to form apertures superposed onthe sensing elements in the sensor layer, where each aperture isconfigured to pass lights to one of the sensing elements. Therefore, thelights reflected from the touch finger may pass through the aperturesand then be received by the sensing elements. The sensing pixels mayfurther include several circuit elements such as transistors andcapacitors, which are omitted in FIG. 4 without influencing theillustrations of the present embodiment.

In order to prevent the moiré pattern appearing in the sensed image, thelight sensing areas, i.e., the apertures formed by the metal wires, maybe turned by an angle. As for each sensing element, the correspondinglight sensing area is an area where the sensing element can receivelights, and the regions outside the light sensing areas may be blockedby the metal wires in the metal layer; hence, each aperture may bedisposed to have an angle deviated from the corresponding sensingelement. This limits the lights received by the sensing elements. Asmentioned above, the lights reflected from the touch finger may passthrough the grille patterns of the display panel and the sensing pixels.Since the aperture on each light path has a turning angle relative tothe grille pattern of the display panel, the received light may belimited in a specific angle that may not be interfered with the patternof the display panel; hence, the problem of moiré pattern may beprevented.

In such a situation, if the sensing pixels and the corresponding sensingelements are arranged as a 2-dimensional array along x-direction andy-direction, the metal wires forming the apertures are disposed alongdirections other than x-direction and y-direction, as can be consideredas being turned from the normal direction. As shown in FIG. 4, the metalwires may be disposed throughout regions other than the apertures of thelight sensing areas. In an embodiment, all of these metal wires may bedisposed along directions other than x-direction and y-direction.

Please note that the above implementation of turning the metal wires andthe apertures is one of various embodiments of the present invention,and the problem of moiré pattern may be prevented by turning anyelements or devices on the light path. Please refer to FIG. 5, which isa schematic diagram of another image sensor 50 according to anembodiment of the present invention. As shown in FIG. 5, the imagesensor 50, which may be a sensor IC, includes a plurality of sensingpixels arranged as a 2-dimensional array. For the purpose of simplicity,only 4 sensing pixels are illustrated. Nevertheless, those skilled inthe art should understand that there maybe hundreds or thousands ofsensing pixels in the image sensor 50. Similar to the image sensor 40,each sensing pixel of the image sensor 50 also includes a sensingelement such as a photodiode. Each sensing element has a light sensingarea defined by an aperture formed by metal wires. In other words, theimage sensor 50 includes a sensor layer and at least one metal layer,where the sensor layer has the sensing elements in the sensing pixels,and the metal layer includes metal wires configured to form aperturessuperposed on the sensing elements in the sensor layer. Each aperture isconfigured to pass lights to one of the sensing elements.

In the image sensor 50, the sensing elements are turned by an angle.This limits the lights received by the sensing elements. As mentionedabove, the lights reflected from the touch finger may pass through thegrille patterns of the display panel and the sensing pixels. Since eachsensing element has an angle relative to the grille pattern of thedisplay panel, the received light may be limited in a specific anglethat may not be interfered with the pattern of the display panel; hence,the problem of moiré pattern may be prevented.

In such a situation, if the sensing pixels and the corresponding sensingelements are arranged as a 2-dimensional array along x-direction andy-direction, a border of the sensing elements may be disposed along adirection other than x-direction and y-direction, as can be consideredas being turned from the normal direction. As shown in FIG. 5, allborders of the sensing elements may be disposed along directions otherthan x-direction and y-direction.

Please refer to FIG. 6, which is a further image sensor 60 according toan embodiment of the present invention. As shown in FIG. 6, the imagesensor 60, which may be a sensor IC, includes a plurality of sensingpixels, each comprising a sensing element such as a photodiode. Thesensing pixels and the corresponding sensing elements are divided into aplurality of groups. The sensing pixels and their sensing elements ineach group are considered as being combined and turned to another angle.Each group is turned individually, to realize the arrangement as shownin FIG. 6. In addition, there may be at least one metal layer superposedon the sensor layer, and the metal wires in the metal layer areconfigured to form apertures corresponding to the positions of thesensing elements with a turning angle.

In such a situation, if the sensing pixel groups are arranged as a2-dimensional array along x-direction and y-direction, the sensingelements in each group may be arranged as a 2-dimensional array alongx′-direction and y′-direction, which are different from the x-directionand y-direction. The borders of the sensing elements maybe disposedalong x′-direction and y′-direction. Correspondingly, the metal wiresforming the apertures superposed on the sensing elements may be disposedalong x′-direction and y′-direction.

Please note that the present invention aims at providing a fingerprintimage sensor which is capable of solving the problem of moiré patternwithout increasing the chip size of the sensor IC. Those skilled in theart may make modifications and alternations accordingly. For example,the moiré effect may be mitigated or eliminated by disposing anyelements on the light path with a turning angle. The turning angle maybe configured arbitrarily, as long as the moiré effect may be mitigated.In an embodiment, an algorithm may be incorporated at the back end todeal with the remaining moiré pattern after being mitigated by theturning disposition. In addition, after the apertures and/or the sensingelements change their directions, the sensed light strength may bereduced due to decreasing of effective sensing area. The reduction ofsensed light strength may be easily compensated in the back-endprocessor.

In the embodiments of the present invention, the direction change ofmetal wires, sensing elements, or both, may be realized by using layouttechniques. With the flexibility of circuit layout in the chip, after asensing element or a group of sensing elements are disposed with aturning angle, other circuit elements and corresponding connection wiresmay be filled in vacant areas outside the sensing elements, so as toefficiently utilize the circuit area in the chip. In such a situation,the implementations of the present invention may not generate a waste onthe usage of circuit area, and thus the chip size may not be expanded.In comparison with the prior art case where the chip size may be up to20.9 mm×15.24 mm, the embodiments of the present invention do notrequire turning of the die, allowing the total chip size to beapproximately equal to the die size, i.e., 18.69 mm×11.31 mm, which hasapproximately 34% reduction of the chip size. As a result, the presentinvention may save the chip area, and the package may be smaller toconform to the chip size, allowing the design of end products to be moreflexible and the usage of space to be more efficiency. The system costsmay also be saved.

To sum up, the present invention provides a fingerprint image sensorwhich is capable of solving the problem of moiré pattern withoutincreasing the chip size of the sensor IC. In an embodiment, the metalwires forming the apertures for passing light to the sensing elementsmay be disposed with a turning angle, i.e., direction change.Alternatively or additionally, the sensing elements may be disposed witha turning angle, i.e., direction change. The direction change may beperformed individually on each sensing pixel, or a plurality of sensingpixels may be combined as a group and turned together. The lightsreflected from the touch finger may pass through the apertures and thenbe received by the sensing elements. The direction change of the metalwires and/or the sensing elements may limit the received light in aspecific angle that may not be interfered with the pattern of thedisplay panel; this prevents the problem of moiré effect. Therefore, themoiré pattern may be mitigated or eliminated by turning the direction ofthe sensing pixels; hence, the chip size may not be expanded and thesystem costs may be reduced.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. An image sensor, comprising: a sensor layer,comprising a plurality of sensing elements arranged as a 2-dimensionalarray along a first direction and a second direction; and at least onemetal layer, each comprising a plurality of metal wires configured toform a plurality of apertures for passing lights to the plurality ofsensing elements; wherein at least one of the plurality of metal wiresforming the plurality of apertures is disposed along a third directiondifferent from the first direction and the second direction.
 2. Theimage sensor of claim 1, wherein none of the plurality of metal wiresforming the plurality of apertures is disposed along the first directionor the second direction.
 3. The image sensor of claim 1, wherein each ofthe plurality of apertures is disposed to have an angle deviated from acorresponding sensing element among the plurality of sensing elements.4. The image sensor of claim 1, wherein each of the plurality ofapertures is configured to pass lights to one of the plurality ofsensing elements.
 5. An image sensor, comprising: a sensor layer,comprising a plurality of sensing elements arranged as a 2-dimensionalarray along a first direction and a second direction; and at least onemetal layer, each comprising a plurality of metal wires configured toform a plurality of apertures for passing lights to the plurality ofsensing elements; wherein a border of the plurality of sensing elementsis disposed along a third direction different from the first directionand the second direction.
 6. The image sensor of claim 5, wherein noneof a plurality of borders of the plurality of sensing elements isdisposed along the first direction or the second direction.
 7. The imagesensor of claim 5, wherein each of the plurality of apertures isconfigured to pass lights to one of the plurality of sensing elements.8. An image sensor, comprising: a sensor layer, comprising a pluralityof sensing elements divided into a plurality of groups, wherein theplurality of groups are arranged as a 2-dimensional array along a firstdirection and a second direction; and at least one metal layer, eachcomprising a plurality of metal wires configured to form a plurality ofapertures for passing lights to the plurality of sensing elements;wherein the sensing elements in each of the plurality of groups arearranged as a 2-dimensional array along a third direction and a fourthdirection, wherein each of the third direction and the fourth directionis different from the first direction and the second direction.
 9. Theimage sensor of claim 8, wherein each of the plurality of metal wiresforming the plurality of apertures is disposed along the third directionor the fourth direction.
 10. The image sensor of claim 8, wherein eachborder of the plurality of sensing elements is disposed along the thirddirection or the fourth direction.